The replacement of an active hydrogen by a trialkylsilyl group reduces the polarity of a compound and decreases the possibility for hydrogen bonding. Consequently, where there is marked intermolecular hydrogen bonding in the parent compound the silylated derivative is usually more volatile. The greatest use of silylation has been for gas chromatography.
Of particular utility among the many trialkyl silylating agents are those having a t-butyldimethylsilyl group. The most common of these agents is t-butyldimethylsilyl chloride which in the presence of a base such as imidazole or pyridine in a solvent such as N,N-dimethylformamide has been successfully used in the analysis of many compounds containing an active hydrogen. Silylating agents having a t-butyldimethylsilyl group are preferred over their trimethylsilyl counterparts because of the ease with which the t-butyldimethylsilyl group can be removed under relatively mild acidic or neutral conditions, and the relative high stability of the t-butyldimethylsilyl derivative to alkaline conditions, to hydrogenolysis and to solvolysis.
While trimethylsilyl reagents such as N,O-bistrimethylsilylacetamide will trimethylsilylate phosphoric acid, boric acid and others, the silylated oxy-anions are unstable and degrade to some extent on a gas chromatograph. The trimethylsilyl derivatives of sulfuric acid and sulfurous acid degrade rapidly and will destroy most gas chromatograph columns after several injections. On the other hand, silylated oxy-anions of sulfuric acid, phosphoric acid, boric acid, phosphorous acid, carbonic acid and the like are not formed at all with t-butyldimethylsilyl chloride even in the presence of a base such as imidazole in N,N-dimethylformamide.
In view of the above, it is an object of the present invention to provide an improved method for analyzing inorganic oxy-anions. Other objects and features will be in part apparent and in part pointed out hereinafter. The invention accordingly comprises the methods hereinafter described, the scope of the invention being indicated in the subjoined claims.